1. Field of the Invention
The present invention relates to a fuel cell power supply system that supplies electric power to a load using both a fuel cell and accumulating means such as a capacitor and a secondary battery.
2. Description of the Related Art
Conventionally, as a power source for a fuel cell vehicle, there is known a power source in which, for example, as shown in FIG. 8, a fuel cell 101 and a capacitor 102 (an electric double layer capacitor) are connected in parallel and this parallel circuit is connected to a driving motor 105 (a load) via a converter 103 and a PDU 4. There is proposed a fuel cell power supply device in which the output of the fuel cell 101 is supplemented with the output of the capacitor 102 when electric power requested by the driving motor suddenly increases (shift to large output in short time is requested), for example, during acceleration of the fuel cell vehicle (see, for example, Japanese Patent Application Laid-Open No. 2004-312964).
It is possible to reduce the number of cells forming a fuel cell stack and realize a reduction in size and cost of a fuel cell by supplementing the output of the fuel cell with the output of a capacitor in this way.
However, in the fuel cell power supply device disclosed in Japanese Patent Application Laid-Open No. 2004-312964, when it is attempted to increase the output of the capacitor, which supplements the output of the fuel cell, in order to secure driving power for the large-power driving motor, since it is necessary to increase the capacity of the capacitor, there is inconvenience in that the weight and the volume of the capacitor increase.
Therefore, in order to prevent this inconvenience, the loading weight and the volume of the capacitor are limited. Then, when shift to large output in short time is requested, for example, during acceleration of the fuel cell vehicle, there is inconvenience in that it is impossible to quickly respond to the request and acceleration performance falls (time for reaching target vehicle speed is long).
Therefore, in order to prevent this inconvenience, there is proposed a fuel cell power supply device in which, for example, as shown in FIG. 9, a fuel cell 201 and a capacitor 202 are connected in parallel, this parallel circuit is connected to a driving motor 206 via a PDU 205, accumulating means (a secondary battery) 203 is connected to the driving motor 206 via a converter 204 and the PDU 205, and the output of the fuel cell 201 and the capacitor 202 is supplemented with the output of the secondary battery 203 (see, for example, Japanese Patent Application Laid-Open No. 2004-14159). This makes it possible to realize a reduction in size and cost of a fuel cell and control the weight and the volume of a capacitor.
However, in the fuel cell battery device disclosed in Japanese Patent Application Laid-Open No. 2004-14159, when it is attempted to increase the output of the secondary battery, which supplements the output of the fuel cell and the capacitor, in order to secure the driving power to the high-power driving motor, it is necessary to increase a loading amount or increase the power density of the secondary battery.
When the secondary battery is set to high power density (e.g., equal to or higher than 3000 w/kg), since an electrode area increases, there is inconvenience in that the size of the secondary battery and the volume of the secondary battery increase. Therefore, in order to prevent this inconvenience, the power density of the secondary battery is reduced (e.g., about 2000 w/kg) to realize a reduction in size of the secondary battery, a margin of the output performance of the secondary battery is lost. As a result, when large output is requested, driving is continued near an output performance limit of the secondary battery and deterioration in durability of the secondary battery due to heat generation is likely to be caused.